Lightweight building block



FIG. 1 is a top plan view of a first embodiment of a building block showing my new design shown broken away to indicate indeterminate length;

FIG. 2 is a side elevation view thereof;

FIG. 3 is an end elevation view thereof;

FIG. 4 is a perspective view thereof;

FIG. 5 is a top plan view of a second embodiment of the building block shown broken away to indicate indeterminate length;

FIG. 6 is a side elevation view thereof;

FIG. 7 is a perspective view thereof; and,

FIG. 8 is a end elevation view thereof.

The dotted lines depict that the building blocks may be of varied lengths and form no part of the claimed designs. 

The ornamental designs for a lightweight building block, as shown and described. 